Map. A map is a collection that has keys, and values for each key. And the term may refer to a function that applies a method to each element in a collection.
In VB.NET, the term "map" does not have a specific meaning, so we must use the Dictionary type and Select function. A lambda expression can be used as an argument to Select.
Collection example. How can we use a map collection in VB.NET? First we must create a new instance of the Dictionary, with its generic type syntax.
Part 1 We add 2 keys, with associated values, to the Dictionary after creating it.
Part 2 When using a Dictionary, we can loop over its keys and values with a For-Each loop.
Part 3 It is possible to access the map at a key, but this will throw an exception if the key is not found.
Part 4 With TryGetValue, we can access a value at a key more safely—if the key is not found, no exception is thrown (False is returned instead).
Module Module1
Sub Main()
' Part 1: create new Dictionary and add 2 keys and values.
Dim map = New Dictionary(Of String, String)()
map.Add("cat", "orange")
map.Add("dog", "brown")
' Part 2: loop over the map.
For Each pair In map
Dim key = pair.Key
Dim value = pair.Value
Console.WriteLine($"{key} / {value}")
Next
' Part 3: access value at key.
Dim result = map("cat")
Console.WriteLine(result)
' Part 4: access value at key with TryGetValue (safer).
Dim result2 = Nothing
If map.TryGetValue("dog", result2)
Console.WriteLine(result2)
End If
End Sub
End Modulecat / orange
dog / brown
orange
brown
Modify array. Another use of the term "map" means to apply a function each element of a collection (like an array). This can be done with the Select function in VB.NET.
Tip We pass a lambda expression with the Function keyword as an argument to the Select Function.
Tip 2 In languages like Python, the "map" function is equivalent to Select() in VB.NET.
Module Module1
Sub Main()
Dim array As String() = { "bird", "fish" }
' Print original array.
Console.WriteLine(String.Join(",", array))
' Call a Function on each element in the array, modifying the element.
Dim result = array.Select(Function (x)
Return x.ToUpper()
End Function).ToArray()
' Print result.
Console.WriteLine(String.Join(",", result))
End Sub
End Modulebird,fish
BIRD,FISH
VB.NET programs can create map collections with a Dictionary, and map elements in collections with the Select function. Mapping things is an essential task in this language.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
